(1) Goals of project: To identify cellular genes required for optimal HIV-1 infection, or involved in HIV-1 pathogenesis. To study the mechanism by which intrathymic HIV-1 infection affects the development of different T cell subsets. To understand how HIV-1 infection leads to high levels of programmed cell in both CD4 and CD8 cells. To apply the knowledge gained towards development of anti-viral therapy which target both viral and cellular genes. (2) Experimental approach: Hu/Scid mice were infected intrathymically with primary isolate of HIV. Thymocytes were separated into various subsets by 3 color stainings and the presence of proviral DNA was determined by quantitative PCR. The role of the negative kinase Chk in fas-mediated apoptosis was determined using a panel of human cell lines lacking Chk, or expressing wild type or mutated Chk. (3) Major Findings: The Hu/Scid model demonstrated that in the infected thymus, that CD3hiCD8+ mature cells are also infected with the virus. The HIV-1 infected CD3hiCD8+ thymocytes also express viral mRNA. These cells are not found in the periphery of infected mice, suggesting intrathymic death. Experiments suggested that the infection may occur during the development of CD4+CD8+ infected cell into single positive CD4 and CD8 cells. The study provides new mechanism for the reported depletion of naive CD8 cells in the periphery of infected individuals, that may contribute to their inability to handle opportunistic infections. Manuscript by Sherley Lee et al. was submitted for publication in J. of Virology. The Chk kinase was found to have strong inhibitory effect on FAS-mediated apoptosis. It is postuated that in HIV-infected patients the intracellular of Chk may be reduced, leading to enhanced susceptibility to apoptosis. Manuscript by Marina Zaitseva et al. was submitted for publication in Nature.